1. Technical Field
This invention is directed to an electrorheological (ER) fluid comprising nonconductive particulate susceptible to ionic and electronic polarization dispersed in an nonconductive fluid.
2. Discussion of Relevant Art
It is generally known that ER fluids exhibit pronounced reversible changes in viscosity and resistance to shear in response to the application of an electric field. Such fluids generally comprise suspensions of finely divided, polarizable particles in an electrically nonconductive oil which can be rapidly and reversibly increased from the liquid to the plastic or solid state under the influence of a sufficiently powerful electric field. Both direct current electric fields and alternating current electric fields may be used for altering the viscosity. Such ER fluids are proposed for use, e.g., in shock absorbers and variable speed accessory drive clutches. As disclosed in U.S. Pat. No. 4,702,855, the particles generally comprise materials like zeolite, silicate, silica gel, and china clay. Fluids containing particles of such materials have the disadvantage that the particles have a tendency to settle.
It is an object of the present invention to provide an ER fluid which maintains a low fluid viscosity in an electric field. It is a further object of the present invention to provide an ER fluid which exhibits strong ER effects in an electric field. It is a further object of the present invention to provide an ER fluid whose particles remain substantially dispersed, avoiding the tendency to settle as is common with conventional ER fluids.